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Kai Luodtcxzyw
Kai Luo
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dtcxzyw
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[InstCombine] Fold (sub (xor X, (sext C)), (sext C)) => (select C (neg X), X) (#79417)
This is useful when computing absdiff. Correctness prove: https://alive2.llvm.org/ce/z/eMbxps, https://alive2.llvm.org/ce/z/SNCWJe. --------- Co-authored-by: Yingwei Zheng <[email protected]>
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‎llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp‎

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@@ -2448,6 +2448,21 @@ Instruction *InstCombinerImpl::visitSub(BinaryOperator &I) {
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}
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}
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{
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// (sub (xor X, (sext C)), (sext C)) => (select C, (neg X), X)
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// (sub (sext C), (xor X, (sext C))) => (select C, X, (neg X))
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Value *C, *X;
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auto m_SubXorCmp = [&C, &X](Value *LHS, Value *RHS) {
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return match(LHS, m_OneUse(m_c_Xor(m_Value(X), m_Specific(RHS)))) &&
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match(RHS, m_SExt(m_Value(C))) &&
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(C->getType()->getScalarSizeInBits() == 1);
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};
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if (m_SubXorCmp(Op0, Op1))
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return SelectInst::Create(C, Builder.CreateNeg(X), X);
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if (m_SubXorCmp(Op1, Op0))
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return SelectInst::Create(C, X, Builder.CreateNeg(X));
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}
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if (Instruction *R = tryFoldInstWithCtpopWithNot(&I))
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return R;
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‎llvm/test/Transforms/InstCombine/sub-xor-cmp.ll‎

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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
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; RUN: opt < %s -passes=instcombine -S | FileCheck %s
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define i64 @sext_xor_sub(i64 %a, i1 %b) {
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; CHECK-LABEL: define i64 @sext_xor_sub(
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; CHECK-SAME: i64 [[A:%.*]], i1 [[B:%.*]]) {
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; CHECK-NEXT: [[TMP1:%.*]] = sub i64 0, [[A]]
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; CHECK-NEXT: [[R:%.*]] = select i1 [[B]], i64 [[TMP1]], i64 [[A]]
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; CHECK-NEXT: ret i64 [[R]]
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;
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%c = sext i1 %b to i64
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%d = xor i64 %a, %c
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%r = sub i64 %d, %c
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ret i64 %r
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}
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define i64 @sext_xor_sub_1(i64 %a, i1 %b) {
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; CHECK-LABEL: define i64 @sext_xor_sub_1(
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; CHECK-SAME: i64 [[A:%.*]], i1 [[B:%.*]]) {
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; CHECK-NEXT: [[TMP1:%.*]] = sub i64 0, [[A]]
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; CHECK-NEXT: [[R:%.*]] = select i1 [[B]], i64 [[TMP1]], i64 [[A]]
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; CHECK-NEXT: ret i64 [[R]]
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;
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%c = sext i1 %b to i64
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%d = xor i64 %c, %a
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%r = sub i64 %d, %c
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ret i64 %r
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}
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define i64 @sext_xor_sub_2(i64 %a, i1 %b) {
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; CHECK-LABEL: define i64 @sext_xor_sub_2(
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; CHECK-SAME: i64 [[A:%.*]], i1 [[B:%.*]]) {
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; CHECK-NEXT: [[TMP1:%.*]] = sub i64 0, [[A]]
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; CHECK-NEXT: [[R:%.*]] = select i1 [[B]], i64 [[A]], i64 [[TMP1]]
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; CHECK-NEXT: ret i64 [[R]]
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;
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%c = sext i1 %b to i64
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%d = xor i64 %a, %c
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%r = sub i64 %c, %d
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ret i64 %r
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}
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define i64 @sext_xor_sub_3(i64 %a, i1 %b) {
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; CHECK-LABEL: define i64 @sext_xor_sub_3(
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; CHECK-SAME: i64 [[A:%.*]], i1 [[B:%.*]]) {
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; CHECK-NEXT: [[TMP1:%.*]] = sub i64 0, [[A]]
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; CHECK-NEXT: [[R:%.*]] = select i1 [[B]], i64 [[A]], i64 [[TMP1]]
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; CHECK-NEXT: ret i64 [[R]]
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;
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%c = sext i1 %b to i64
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%d = xor i64 %c, %a
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%r = sub i64 %c, %d
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ret i64 %r
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}
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; Sext non boolean type.
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define i64 @sext_non_bool_xor_sub(i64 %a, i8 %b) {
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; CHECK-LABEL: define i64 @sext_non_bool_xor_sub(
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; CHECK-SAME: i64 [[A:%.*]], i8 [[B:%.*]]) {
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; CHECK-NEXT: [[C:%.*]] = sext i8 [[B]] to i64
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; CHECK-NEXT: [[D:%.*]] = xor i64 [[C]], [[A]]
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; CHECK-NEXT: [[R:%.*]] = sub i64 [[D]], [[C]]
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; CHECK-NEXT: ret i64 [[R]]
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;
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%c = sext i8 %b to i64
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%d = xor i64 %a, %c
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%r = sub i64 %d, %c
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ret i64 %r
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}
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define i64 @sext_non_bool_xor_sub_1(i64 %a, i8 %b) {
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; CHECK-LABEL: define i64 @sext_non_bool_xor_sub_1(
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; CHECK-SAME: i64 [[A:%.*]], i8 [[B:%.*]]) {
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; CHECK-NEXT: [[C:%.*]] = sext i8 [[B]] to i64
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; CHECK-NEXT: [[D:%.*]] = xor i64 [[C]], [[A]]
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; CHECK-NEXT: [[R:%.*]] = sub i64 [[D]], [[C]]
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; CHECK-NEXT: ret i64 [[R]]
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;
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%c = sext i8 %b to i64
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%d = xor i64 %c, %a
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%r = sub i64 %d, %c
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ret i64 %r
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}
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; Different boolean values.
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define i64 @sext_diff_i1_xor_sub(i64 %a, i1 %b, i1 %c) {
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; CHECK-LABEL: define i64 @sext_diff_i1_xor_sub(
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; CHECK-SAME: i64 [[A:%.*]], i1 [[B:%.*]], i1 [[C:%.*]]) {
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; CHECK-NEXT: [[D:%.*]] = sext i1 [[B]] to i64
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; CHECK-NEXT: [[E_NEG:%.*]] = zext i1 [[C]] to i64
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; CHECK-NEXT: [[R:%.*]] = add nsw i64 [[E_NEG]], [[D]]
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; CHECK-NEXT: ret i64 [[R]]
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;
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%d = sext i1 %b to i64
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%e = sext i1 %c to i64
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%f = xor i64 %a, %d
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%r = sub i64 %d, %e
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ret i64 %r
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}
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define i64 @sext_diff_i1_xor_sub_1(i64 %a, i1 %b, i1 %c) {
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; CHECK-LABEL: define i64 @sext_diff_i1_xor_sub_1(
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; CHECK-SAME: i64 [[A:%.*]], i1 [[B:%.*]], i1 [[C:%.*]]) {
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; CHECK-NEXT: [[D:%.*]] = sext i1 [[B]] to i64
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; CHECK-NEXT: [[E_NEG:%.*]] = zext i1 [[C]] to i64
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; CHECK-NEXT: [[R:%.*]] = add nsw i64 [[E_NEG]], [[D]]
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; CHECK-NEXT: ret i64 [[R]]
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;
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%d = sext i1 %b to i64
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%e = sext i1 %c to i64
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%f = xor i64 %d, %a
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%r = sub i64 %d, %e
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ret i64 %r
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}
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; (sext C) has multiple uses.
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define i64 @sext_multi_uses(i64 %a, i1 %b, i64 %x) {
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; CHECK-LABEL: define i64 @sext_multi_uses(
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; CHECK-SAME: i64 [[A:%.*]], i1 [[B:%.*]], i64 [[X:%.*]]) {
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; CHECK-NEXT: [[C:%.*]] = sext i1 [[B]] to i64
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; CHECK-NEXT: [[TMP1:%.*]] = sub i64 0, [[A]]
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; CHECK-NEXT: [[E:%.*]] = select i1 [[B]], i64 [[TMP1]], i64 [[A]]
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; CHECK-NEXT: [[F:%.*]] = mul i64 [[C]], [[X]]
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; CHECK-NEXT: [[R:%.*]] = add i64 [[F]], [[E]]
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; CHECK-NEXT: ret i64 [[R]]
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;
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%c = sext i1 %b to i64
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%d = xor i64 %a, %c
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%e = sub i64 %d, %c
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%f = mul i64 %x, %c
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%r = add i64 %f, %e
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ret i64 %r
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}
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; (xor X, (sext C)) has multiple uses.
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define i64 @xor_multi_uses(i64 %a, i1 %b, i64 %x) {
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; CHECK-LABEL: define i64 @xor_multi_uses(
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; CHECK-SAME: i64 [[A:%.*]], i1 [[B:%.*]], i64 [[X:%.*]]) {
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; CHECK-NEXT: [[C:%.*]] = sext i1 [[B]] to i64
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; CHECK-NEXT: [[D:%.*]] = xor i64 [[C]], [[A]]
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; CHECK-NEXT: [[E:%.*]] = sub i64 [[D]], [[C]]
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; CHECK-NEXT: [[F:%.*]] = mul i64 [[D]], [[X]]
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; CHECK-NEXT: [[R:%.*]] = add i64 [[F]], [[E]]
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; CHECK-NEXT: ret i64 [[R]]
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;
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%c = sext i1 %b to i64
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%d = xor i64 %a, %c
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%e = sub i64 %d, %c
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%f = mul i64 %x, %d
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%r = add i64 %f, %e
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ret i64 %r
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}
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define i64 @absdiff(i64 %a, i64 %b) {
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; CHECK-LABEL: define i64 @absdiff(
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; CHECK-SAME: i64 [[A:%.*]], i64 [[B:%.*]]) {
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; CHECK-NEXT: [[C:%.*]] = icmp ult i64 [[A]], [[B]]
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; CHECK-NEXT: [[D:%.*]] = sub i64 [[A]], [[B]]
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; CHECK-NEXT: [[TMP1:%.*]] = sub i64 0, [[D]]
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; CHECK-NEXT: [[RES:%.*]] = select i1 [[C]], i64 [[TMP1]], i64 [[D]]
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; CHECK-NEXT: ret i64 [[RES]]
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;
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%c = icmp ult i64 %a, %b
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%c.ext = sext i1 %c to i64
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%d = sub i64 %a, %b
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%may.rev = xor i64 %c.ext, %d
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%res = sub i64 %may.rev, %c.ext
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ret i64 %res
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}
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; Commuted xor operands compared to absdiff.
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define i64 @absdiff1(i64 %a, i64 %b) {
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; CHECK-LABEL: define i64 @absdiff1(
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; CHECK-SAME: i64 [[A:%.*]], i64 [[B:%.*]]) {
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; CHECK-NEXT: [[C:%.*]] = icmp ult i64 [[A]], [[B]]
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; CHECK-NEXT: [[D:%.*]] = sub i64 [[A]], [[B]]
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; CHECK-NEXT: [[TMP1:%.*]] = sub i64 0, [[D]]
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; CHECK-NEXT: [[RES:%.*]] = select i1 [[C]], i64 [[TMP1]], i64 [[D]]
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; CHECK-NEXT: ret i64 [[RES]]
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;
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%c = icmp ult i64 %a, %b
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%c.ext = sext i1 %c to i64
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%d = sub i64 %a, %b
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%may.rev = xor i64 %d, %c.ext
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%res = sub i64 %may.rev, %c.ext
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ret i64 %res
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}
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; Use ugt as compare cond.
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define i64 @absdiff2(i64 %a, i64 %b) {
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; CHECK-LABEL: define i64 @absdiff2(
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; CHECK-SAME: i64 [[A:%.*]], i64 [[B:%.*]]) {
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; CHECK-NEXT: [[C:%.*]] = icmp ugt i64 [[A]], [[B]]
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; CHECK-NEXT: [[D:%.*]] = sub i64 [[B]], [[A]]
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; CHECK-NEXT: [[TMP1:%.*]] = sub i64 0, [[D]]
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; CHECK-NEXT: [[RES:%.*]] = select i1 [[C]], i64 [[TMP1]], i64 [[D]]
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; CHECK-NEXT: ret i64 [[RES]]
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;
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%c = icmp ugt i64 %a, %b
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%c.ext = sext i1 %c to i64
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%d = sub i64 %b, %a
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%may.rev = xor i64 %d, %c.ext
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%res = sub i64 %may.rev, %c.ext
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ret i64 %res
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}

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